Tagged Questions

In set theory, the union (denoted by ∪) of a collection of sets is the set of all distinct elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other.

When attempting to union multiple polygons with Shapely 1.5.6 in Python 2.7.9, using GEOS 3.4.2, I get the following error in the underlying C++ code:
Assertion failed: (!"should never be reached"), ...

We have a set of thousands of points and want to group all of those which are within 100m distance from each other (to get the centroid from each group). A first idea was to build 100m buffers around ...

I have a month's worth of snowfall contoured polygons in one feature class. Polygons represent one day and has a field called SNOWFALL. How can I display the total snowfall for the month? I have the ...

I'm trying to execute a 'dissolve' operation in PostGIS using the ST_Union command.
The input layer is admittedly quite large and complex. By 'large' I mean 57,771 features, with number of vertices ...

I have 14 polygon layers. I have plotted them as transparent layers, so I can get a final layer with 6 different colours, which represent different categories. I want to create a new layer made by the ...

I would like to do adjacency tests on a parcel (polygons) layer and merge them if they fit certain criteria (could be size). Per the picture below, I would like to merge polygons 1,2,3 and 4, but not ...

I have found some unexpected behavior of ArcGIS union tool. My assumption was that this tool will never add any new vertex to the output layer, but this was not the case.
I have run the ArcGIS union ...

I have several land use layers (vector polygons) that all contain a field about land use in different classification systems and would like to combine them to a single classification. I would like to ...

I'm using GeoDjango (but I guess this is from the geos library).
I have a set of polygons that compose a city surface and I want to merge them into a single one.
The code looks like this:
polygons = ...

I need a union function for a lot of polygon layers (protected areas of all kind, nature, water etc.) comparable to the union function in ArcGIS. I have only the desktop version from ArcGIS and so it ...

I'm trying to use PostGIS to do a 'union' of polygons. When I Googled "PostGIS Union", I found the ST_Union function, which performs what I would call a 'dissolve,' not a Union. What I actually want ...

I have been working through an ESRI Tutorial for GIS Analysis. One of the tasks is to Union two feature classes (Flood Areas and Land Use) which are both polygon feature classes.
Each time I attempt ...

I have a polygon feature class in which the polygons frequently overlap each other. I want to find all of the unique combinations of overlapping polygons within that feature class. I believe I want to ...

I want to calculate the union/merge two overlapping polygons using ogr2ogr (as I have 300+ to do). I want the output to be the same as you would get if you used the 'Merge shapefiles to one' command ...

tl;dr: I have a fgdb w/ 800k tiny polygons representing high risk flood areas. I need to sum the area of these polygons within each administrative boundary (HUCs) and have a ratio per huc of high risk ...

I want to combine different layers into one but I still want to identify different layers in the new combined layer. Union is best for this, but it doesn't allow me to combine more than two layers. I ...

I've been reading a number of related threads about ST_Union, ST_SnapToGrid and ST_Dump but I haven't been able to solve my problem.
The problem is I am trying to merge Tiger/line census tracts that ...

I have approximately 1 million polygons that have been split by lines. However, this has caused one half of a polygon to be separated by approximately 50cm from its other half.
After doing a lot of ...

In PostGSI, is there anyway to turn a GEOMETRYCOLLECTION into a MULTIPOLYGON by dropping all non-POLYGONs/non-MULTIPOLYGONs?
I'm doing a query that cuts a bunch of geometries (using ST_Intersection) ...

I'm using OGR to perform a union using UnionCascaded. All my polygons have been created by GDAL polygonize which ensures that all polygons follow pixel edges and should therefore align nicely. But I ...

I'm trying to union US State level upper- and lower-level government boundaries in such a way that generates one PostGIS table with both the upper and lower level names for each shape.
In my example ...

I've decided to move to PostGIS to merge polygons rather than spend hours doing in in QGIS. However, I'm hitting an issue where the results of an ST_Union query are being stored, or at least outputted ...

I have a hand-digitized coverage stored in postgis. There, I have a few shiver-polygons I would like to get rid of by including them into one of the neighbouring polygons.
are there any commands that ...

We have collected millions of cell phone strength readings. I am trying to group points of the same strenght that are within a distance of each other in to a polygon. I asked on the
postgis mailing ...

I have 4 vector shapefile that I would like to join/merge, without worrying about attributes.
Here are the shapefiles.
I would like to do an union and a spatial dissolve, but everytime I do a dissolve ...